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Income Taxes - Additional Information (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Income Taxes [Line Items] |  |  |
Securities transactions income tax (benefit) expense | $ (21,000) | $ 3,200,000 | $ 574,000
Recognition of interest and penalties related to unrecognized tax benefits | $ 0 | $ 0 | $ 0
Earliest Tax Year [Member] |  |  |
Income Taxes [Line Items] |  |  |
Year under examination | 2014 |  |
Latest Tax Year [Member] |  |  |
Income Taxes [Line Items] |  |  |
Year under examination | 2016 |  |

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- Definition Income taxes. + References No definition available. + Details
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- Definition Tax year that remains open to examination under enacted tax laws, in CCYY format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32718-109319 + Details
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- Definition Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32718-109319 + Details
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